Field of the Invention
The present invention is generally directed toward nanocatalysts and methods of using such catalysts to synthesize aromatic hydrocarbon compounds from carbon dioxide and hydrogen mixtures under relatively mild reaction conditions. Particularly, the catalyst comprises an Fe/Fe3O4 nanocatalyst that may be supported on a non-reactive support material such as a zeolite or alumina. The aromatic hydrocarbon compounds produced are suitable for direct usage as fuel without need for further refining.
Description of the Prior Art
The diminishing fossil fuel reserves and ever-increasing CO2 emissions have created great concern amongst the scientific community. Since the industrial revolution, a significant increase of CO2 concentration in the atmosphere has been witnessed due to the combustion of carbon-rich fossil fuels, consequently, leading to global warming and drastic climate changes. As a result, the quest for renewable and cleaner energy sources to meet the fast population and economic growth is more urgent than ever before. Being the most abundant carbon source in earth's atmosphere, CO2 can be used as a cheap and non-toxic C1 building block in many chemical processes. Hydrogenation of CO2 to produce methanol and dimethylether (DME), as well as hydrocarbons is attractive, not only because these products are excellent fuels for internal combustion engines, but also because the whole process is considered to be cleaner, sustainable, and carbon-neutral (for example, using CO2 from atmosphere, H2 from water splitting and sunlight for energy). However, their chemical and physical properties, are inferior to conventional gasoline. Our distribution systems were developed for liquid fuel. It is easier and less costly to use the existing distribution infrastructure instead of building a new distribution system for methane or hydrogen. Liquid fuels are also safer than gaseous fuels: 1000 atmospheres (14,696 psi) of CH4 or H2 have the same density than 1 L of liquid fuels at room temperature. However, liquid fuels are much less in danger of explosion during accidents.
Although methane has a high octane number (120), it is not useful for classic combustion engines. Mesitylene, octane number: 110, xylenes: 115-120, toluene: 111 make excellent components of high-octane fuel (86 to 92 in the US). Finally, whereas the long-term storage of hydrogen is very difficult, a mixture of aromatic hydrocarbons can be easily stored for fuel or synthesis application.
Iron-based heterogeneous catalysts have been intensively studied for the CO2 hydrogenation reaction. Earlier research showed that bulk iron or iron oxides catalyze CO2 hydrogenation, which mainly produce methane as product. These catalysts were rapidly deactivated due to carbon deposition. Doping of promoters such as potassium, manganese, and copper had significant effect on both the reactivity and selectivity of the iron-based catalysts. Higher olefins and aliphatic hydrocarbons, as well as improved CO2 conversion, were achieved. Al2O3 was found to be an excellent structure promoter to sustain the catalyst activity of iron-based catalysts by preventing sintering of active particles during the reaction. When using zeolites as solid supports, the product's distribution was highly dependent on the structure and acidity of the zeolites. The iron-zeolite composites were also reported as dual functional catalysts that promoted multi-step transformation for CO2 hydrogenation.
In spite of all the efforts during the last decades, the direct formation of aromatic hydrocarbons in a one-step reaction from carbon dioxide, without forming aliphatic hydrocarbons first, remains elusive.